Liquid oligomers containing unsaturation

ABSTRACT

The liquid oligomeric compositions of this invention are made by the Michael addition reaction of acetoacetate functional donor compounds with multifunctional acrylate receptor compounds where the equivalent ratios of multifunctional acrylate to acetoacetate vary from ≧1:1 to ≧13.2:1 depending on the functionality of both multifunctional acrylate and acetoacetate. Unuseable gelled or solid oligomer products occur below the claimed ranges. The liquid oligomers of this invention are further crosslinked to make coatings, laminates and adhesives.

FIELD OF THE INVENTION

This invention relates to liquid oligomers containing unsaturation whichcan be crosslinked using ultraviolet light without adding costlyphotoinitiators. Films made from the crosslinked oligomers of theinventions are used as protective or decorative coatings on varioussubstrates. The oligomers can be added to other resins used in adhesivesor composites.

BACKGROUND OF THE INVENTION

Acrylate, methacrylate and other unsaturated monomers are widely used incoatings, adhesives, sealants, and elastomers, and may be crosslinked byultraviolet light radiation or peroxide initiated free radical cure.These are typically low molecular weight multifunctional compounds whichmay be volatile or readily absorbed through skin and can cause adversehealth effects. Functionalized polymers may overcome some of thesedrawbacks; generally, polymers are nonvolatile compounds, not readilyabsorbed through skin. However, multistep syntheses may be required, lowfunctionality may be detrimental to reactivity and final properties, andcatalyst or initiator may be required to effect crosslinking.

The Michael addition of acetoacetate donor compounds to multiacrylatereceptor compounds to make crosslinked polymers has been described inthe literature. For example, Mozner and Rheinberger reported the Michaeladdition of acetoacetates having a β-dicarbonyl group to triacrylatesand tetracrylates. Macromolecular Rapid Communications 16, 135-138(1995). The products formed were crosslinked gels. In one of thereactions, Mozner added one mole of trimethylol propane triacrylate(TMPTA) having 3 functional groups to one mole of polyethylene glycol(600 molecular weight) diacetoacetate (PEG600-DAA) having two functionalgroups. (Each "acetoacetate functional group" reacts twice, thus eachmole of diacetoacetate has four reactive equivalents.) ##STR1## MoleRatio of TMPTA: PEG 600 DAA=1:1 Ratio of acrylate: acetoacetatefunctional groups=3:2

Ratio of reactive equivalents=3:4

BROAD DESCRIPTION OF THE INVENTION

This invention is the discovery that certain soluble liquiduncrosslinked oligomers, made by one step Michael addition ofacetoacetates to multiacrylates, can be further crosslinked usingultraviolet light without using costly photoinitiators.

We have discovered that when precise proportions of multiacrylateacceptor compounds to acetoacetate donor compounds are combined using abasic catalyst, liquid oligomeric compositions are the product. Ifproportions below the claimed ranges are used, crosslinked gels or solidproducts are made which are not useful for the purposes of thisinvention because only un-gelled, uncrosslinked liquid oligomers willfurther crosslink without adding photoinitiators. In addition, theliquid oligomer compositions of this invention, since they are liquids,can readily be applied to various substrates using conventional coatingtechniques such as roll or spray prior to ultraviolet light cure.

BRIEF DESCRIPTION OF THE DRAWING

The graph illustrates that ratios below the three curves were unuseablegelled materials outside the scope of the invention. Ratios on or abovethe curves are the liquid oligomers of this invention.

DETAILED DESCRIPTION OF THE INVENTION

Among the multiacrylates used to make the oligomers of this inventionare diacrylates, triacrylates, and tetraacrylates. ##STR2##

The Michael addition reaction is catalyzed by a strong base;diazabicycloundecene (DBU) is sufficiently strong and readily soluble inthe monomer mixtures. Other cyclic amidines, for examplediazabicyclo-nonene (DBN) and guanidines are also suitable forcatalyzing this polymerization.

Michael addition of a methacrylate functional β-dicarbonyl compound,2-acetoacetoxyethyl methacrylate (AAEM), to diacrylate monomer yieldsliquid linear polyesters with reactive pendant methacrylate groups,which can be crosslinked in a subsequent curing reaction. As theacrylate and acetoacetate are mutually reactive and the methacrylate isinert under the conditions of the Michael addition, a highlyfunctionalized (one methacrylate per repeat unit), liquid uncrosslinkedpolymer can be obtained in a one-step, ambient temperature, solventlessreaction. The high selectivity of the Michael reaction permits the useof monomers such as styrene and methyl methacrylate as inert solvents togive low-viscosity systems that are easily incorporated into a varietyof laminating resins.

In the following Examples all parts are by weight unless otherwiseindicated. In addition, all references mentioned herein are specificallyincorporated by reference.

A series of experiments defined the proportions of multi-acrylate toβ-dicarbonyl acetoacetate which separate the liquid oligomer products ofthis invention from the gel or solid products of the prior art.

Synthetic Procedure

An example of resin synthesis is as follows. Trimethylolpropanetriacrylate (TMPTA) 59.2 g and diazabicycloundecene (DBU) 0.4 g wereweighed into a 500 ml 3-neck round bottom flask equipped with amechanical stirrer and addition funnel. Ethyl acetoacetate (EM) 13.0 gwas weighed into the addition funnel. The TMPTA and DBU were mixed for 5minutes prior to addition of the EAA. EAA was then added dropwise to thestirred TMPTA/DBU mixture over a 15 minute period. The solution warmedto 54 degrees Centigrade after addition of EAA was complete. After theexotherm subsided in 100 minutes a viscous yellow liquid was obtainedwhich did not gel upon standing.

The same general procedure can be employed for a variety of combinationsof acrylate and acetoacetate functional reactants, provided theequivalent ratio of acrylate:acetoacetate is sufficient to yield liquid,uncrosslinked products. For particularly exothermic or large scalereactions, controlled, gradual addition of acetoacetate and/or coolingof the reaction may be required to prevent premature, thermallyinitiated crosslinking of acrylate functional groups.

                  TABLE 1                                                         ______________________________________                                        Acetoacetate/Acrylate Mixtures                                                aceto-                  mole equiv                                                                              weight reaction                             acetate acrylate                                                                              f ratio ratio                                                                              ratio                                                                              ratio  product                              ______________________________________                                        A   ethyl   hexane- 2:2   1:1  2:2  36.5:63.5                                                                            viscous                                        diol                           liquid*                            B   ethyl   penta-  2:4   1:10  1:20                                                                               3.6:96.4                                                                            viscous                                        ery-                           liquid*                                        thritol                                                           C   butane- hexane- 4:2   1:1  2:1  53.3:46.7                                                                            crosslinked                            diol    diol                           gel**                              D   penta-  penta-  8:4   1:10 1:5  11.8:88.2                                                                            crosslinked                            ery-    ery-                           gel**                                  thritol thritol                                                           ______________________________________                                         *soluble in methyl ethyl ketone (MEK) at room temperature.                    **insoluble in refluxing methyl ethyl ketone.                            

A and B made useful oligomers of the inventor. C and D made crosslinkedgels which are outside the invention.

                  TABLE 2                                                         ______________________________________                                        Reactions of diacrylate acceptor with acetoacetate-functional donors.                          Func-                                                                         tion-        Equiv-       Reac-                                               ality  Mole  alent Weight tion                               Acceptor                                                                             Donor     ratio  ratio ratio ratio  product                            ______________________________________                                        TRPGDA MeOAcAc   2:2    1:1   1:1   72.1:27.9                                                                            sol                                TRPGDA EtOAcAc   2:2    1:1   1:1   69.8:30.2                                                                            sol                                TRPGDA aceto-    2:2    1:1   1:1   62.9:37.1                                                                            sol                                       acetanilide                                                            TRPGDA butanediol                                                                              2:4    7.7:1 3.9:1 90:10  sol                                       di-OAcAc                                                               TRPGDA           2:4    4.9:1 24:1  85:15  gel                                TRPGDA           2:4    3.44:1                                                                              1.7:1 80:20  gel                                TRPGDA cyclohexane                                                                             2:4    19.8:1                                                                              9.9:1 95:05  sol                                       dimethanol                                                                    di-                                                                    TRPGDA di-OAcAc  2:4    13.8:1                                                                              6.9:1 93:7   sol                                TRPGDA           2:4    94:1  4.7:1 90:10  gel                                TRPGDA           2:4    5.9:1 2.95:1                                                                              85:15  gel                                TRPGDA           2:4    4.2:1 2.1:1 80:20  gel                                TRPGDA neopentyl 2:4    8.2:1 4.1:1 90:10  sol                                       glycol                                                                 TRPGDA di-OAcAc  2:4    5.1:1 2.6:1 85:15  sol                                TRPGDA           2:4    3.6:1 1.8:1 80:20  gel                                TRPGDA TONE      2:6    16.6:1                                                                              5.5:1 90:10  sol                                       0301 tri-                                                                     OAcAc                                                                  TRPGDA           2:6    10.4:1                                                                              3.5:1 85:15  gel                                TRPGDA           2:6    7.4:1 2.5:1 80:20  gel                                TRPGDA glycerin  2:6    10.3:1                                                                              3.4:1 90:10  sol                                       tri-OAcAc                                                              TRPGDA           2:6    6.5:1 2.2:1 85:15  gel                                TRPGDA           2:6    4.6:1 1.5:1 80:20  gel                                TRPGDA pentaery- 2:8    14.2:1                                                                              3.5:1 90:10  sol                                       thritol                                                                       tetra-OAcAc                                                            TRPGDA           2:8    8.9:1 2.2:1 85:15  gel                                TRPGDA           2:8    6.3:1 1.6:1 80:20  gel                                ______________________________________                                    

Review of Table 2 shows that certain diacrylate-acetoacetate equivalentratios make sol or liquid oligomers of the invention.

                  TABLE 3                                                         ______________________________________                                        Reactions of triacrylate acceptor with acetoacetate-functional donors.                         Func-                                                                         tion-        Equiv-       Reac-                                               ality  Mole  alent Weight tion                               Acceptor                                                                             Donor     ratio  ratio ratio ratio  product                            ______________________________________                                        TMPTA  EtOAcAc   3:2    2:1   3:1   82:18  sol                                TMPTA  EtOAcAc   3:2    3:2   2.25:1                                                                              77.4:22.6                                                                            sol                                TMPTA  EtOAcAc   3:2    4:3   2:1   75.2:24.8                                                                            gel                                TMPTA  butanediol                                                                              3:4    7.8:1 5.9:1 90:10  sol                                       di-OAcAc                                                               TMPTA            3:4    4.9:1 3.7:1 85:15  gel                                TMPTA            3:4    3.5:1 2.6:1 80:20  gel                                TMPTA  cyclohexane                                                                             3:4    9.5:1 7.1:1 90:10  sol                                       dimethanol                                                                    di-                                                                    TMPTA  di-OAcAc  3:4    6.0:1 4.5:1 85:15  gel                                TMPTA            3:4    4.2:1 3.2:1 80:20  gel                                TMPTA  neopentyl 3:4    8.3:1 6.2:1 90:10  sol                                       glycol                                                                 TMPTA  di-OAcAc  3:4    5.2:1 3.9:1 85:15  gel                                TMPTA            3:4    3.7:1 2.8:1 80:20  gel                                TMPTA  TONE      3:6    16.8:1                                                                              8.4:1 90:10  sol                                       0301 tri-                                                                     OAcAc                                                                  TMPTA            3:6    10.6:1                                                                              5.3:1 85:15  gel                                TMPTA  glycerin  3:6    14.3:1                                                                              7.2:1 92.5:7.5                                                                             sol                                       tri-OAcAc                                                              TMPTA            3:6    10.5:1                                                                              52:1  90:10  gel                                TMPTA  pentaery- 3:8    30.3:1                                                                              11.4:1                                                                              95:5   sol                                       thritol                                                                       tetra-                                                                        OAcAc                                                                  TMPTA            3:8    19.7:1                                                                              7.4:1 92.5:7.5                                                                             sol                                TMPTA            3:8    14.4:1                                                                              5.4:1 90:10  gel                                ______________________________________                                    

Review of Table 3 shows that certain triacrylate:acetoacetate ratiosmake sol or liquid oligomers of the invention.

                  TABLE 4                                                         ______________________________________                                        Reactions of tetraacrylate acceptor with acetoacetate-functional donors.                       Func-                                                                         tion-        Equiv-       Reac-                                               ality  Mole  alent Weight tion                               Acceptor                                                                             Donor     ratio  ratio ratio ratio  product                            ______________________________________                                        PETA   EtOAcAc   4:2    3.3:1 6.6:1 90:10  sol                                PETA   EtOAcAc   4:2    2:1   4.0:1 84.4:15.6                                                                            gel                                PETA   EtOAcAc   4:2    1:1   2:1   73:27  gel                                PETA   butanediol                                                                              4:4    13.9:1                                                                              13.9:1                                                                              95:5   sol                                       di-                                                                           OAcAc                                                                  PETA             4:4    9.7:1 9.7:1 93:7   sol                                PETA             4:4    6.6:1 6.6:1 90:10  gel                                PETA   cyclohexane                                                                             4:4    16.8:1                                                                              16.8:1                                                                              95:5   sol                                       dimethanol                                                                    di-                                                                    PETA   di-OAcAc  4:4    8.0:1 8:1   90:10  gel                                PETA   neopentyl 4:4    14.7:1                                                                              14.7:1                                                                              95:5   sol                                       glycol                                                                 PETA   di-OAcAc  4:4    10.3:1                                                                              10.3:1                                                                              93:7   sol                                PETA             4:4    7.0:1 7:1   90:10  gel                                PETA   TONE      4:6    29.8:1                                                                              19.9:1                                                                              95:5   sol                                       0301 tri-                                                                     OAcAc                                                                  PETA             4:6    20.8:1                                                                              13.9:1                                                                              93:7   sol                                PETA             4:6    14.1:1                                                                              9.4:1 90:10  gel                                PETA   glycerin  4:6    18.6:1                                                                              12.4:1                                                                              95:5   sol                                       tri-OAcAc                                                              PETA             4:6    12.1:1                                                                              8:1   92.5:7.5                                                                             gel                                PETA   pentaery- 4:8    65.7:1                                                                              32.9:1                                                                              98:2   sol                                       thritol                                                                       tetra-                                                                        OAcAc                                                                  PETA             4:8    43.3:1                                                                              21.7:1                                                                              97:3   sol                                PETA             4:8    32.2:1                                                                              16.1:1                                                                              96:4   sol                                PETA             4:8    25.5:1                                                                              12.7:1                                                                              95:5   sol                                PETA             4:8    17.8:1                                                                              8.9:1 93:7   gel                                PETA             4:8    12.1:1                                                                              6:1   90:10  gel                                ______________________________________                                    

Review of Table 4 shows that certain tetracrylate:acetoacetate ratiosmake sol or liquid oligomers of the invention.

In order to demonstrate ultraviolet light crosslinking of these liquidoligomers, samples containing 1% (wt) Irgacure 500 photoinitiator and 0%photoinitiator were applied to release liner and spread to a thicknessof 1.5 mil. Specimens were cured on a Fusion Systems Corp. uv curingunit, using an H-bulb and belt speed of 20-25 feet/minute; all formedtransparent, flexible, nearly colorless films. Samples of each film wereweighed, immersed in acetone (a good solvent for the uncured resins) atroom temperature for 48 hours, blotted dry and re-weighed to determinesolvent uptake. Specimens were then dried to constant weight in a vacuumoven at 80° C. to determine gel fractions; these values are listed inthe table 5 below.

                  TABLE 5                                                         ______________________________________                                        Solvent Uptake and Gel Fractions of UV Cured Methacrylate                     Functional Polyesters.                                                                 Solvent             Solvent                                                   Uptake, %                                                                              Gel Fraction                                                                             Uptake, %                                                                             Gel Fraction                                      (Irgacure                                                                              (Irgacure 500,                                                                           (No Photo-                                                                            (No Photo-                               DIACRYLATE                                                                             500, 1%) 1%)        initiator)                                                                            initiator)                               ______________________________________                                        NPG      18       94%         9      96%                                      PEG 200  19       96%        18      94%                                      Hexanediol                                                                             12       96%         9      96%                                      Triethylene                                                                            16       95%        19      96%                                      glycol                                                                        ______________________________________                                    

These results confirm that the products are crosslinked and indicate nosignificant difference between products cured with or without addedphotoinitiator. This suggests that the pendant methyl ketonesubstituents serve as an internal or "built in" photoinitiator. Tofurther demonstrate the role of methyl ketone substituents in the uvcure of these resins, three acrylate terminal resins were prepared fromneopentyl glycol diacrylate and various b-dicarbonyl compounds in a 5:4molar ratio. β-dicarbonyl compounds included acetylacetone (2 methylketones per molecule), ethyl acetoacetate (1 ketone/molecule) anddiethyl malonate (no ketones). UV cure was performed as before, withoutadded photoinitiator. Resins containing acetylacetone or ethylacetoacetate cured to soft, tacky films. Such films are useful inprotective or decorative coatings on wood, or metal substrates. Theresin containing diethyl malonate failed to cure, remaining liquid.

We claim:
 1. A liquid oligomeric composition shelf stable for more thanone month having residual pendant unsaturated acrylate groups, useful asa coating when further polymerized comprising the organic solubleungelled uncrosslinked Michael addition reaction product of:a) excessdiacrylate acceptor, triacrylate acceptor, or tetraacrylate acceptor,and b) an acetoacetate donor, having equivalent ratios ofi) diacrylateacceptor:acetoacetate donor of≧1:1 where acetoacetate functionality=2,≧4.5:1 where acetoacetate functionality=4, ≧4.5:1 where acetoacetatefunctionality=6, ≧3.5:1 where acetoacetate functionality=8, ii)triacrylate acceptor: acetoacetate donor of≧2.25 where acetoacetatefunctionality=2, ≧6.4:1 where acetoacetate functionality=4, 7.8:1 whereacetoacetate functionality=6, 7.4:1 where acetoacetate functionality=8,iii) a tetraacrylate acceptor: acetoacetate donor of≧6.6 whereacetacetate functionality=2, ≧12.3:1 where acetoacetate functionality=4,≧13.2:1 where acetoacetate functionality=6, ≧12.7:1 where acetoacetatefunctionality=8.
 2. The composition of claim 1 wherein said reaction iscarried out in the presence of a strong base.
 3. The composition ofclaim 1 wherein said diacrylate is:diethylene glycol diacrylate,ethoxylated bisphenol A diacrylate, 1,6-hexanediol diacrylate, neopentylglycol diacrylate, polyethylene glycol (Mn200) diacrylate, polyethyleneglycol (Mn400) diacrylate, propoxylated neopentyl glycol diacrylate,tetraethylene glycol diacrylate, triethylene glycol diacrylate, ortripropylene glycol diacrylate.
 4. The composition of claim 1 whereinsaid triacrylate is:trimethylolpropane triacrylate, ethoxylatedtrimethylolpropane triacrylate, tris(2-hydroxyethyl) isocyanuratetriacrylate, propoxylated glyceryl triacrylate or pentaerythritoltriacrylate.
 5. The composition of claim 1 wherein said tetracraylate ispentaerythritol tetraacrylate.
 6. The composition of claim 1 whereinacetoacetates having 2 reactive functional groups per molecule areethylacetoacetate, t-butylacetoacetate, methyl acetoacetate, 2-ethylhexylacetoacetate, lauryl acetoacetate, acetoacetanilide,2-acetoacetoxylethyl methacrylate or allyl acetoacetate.
 7. Thecomposition of claim 1 wherein acetoacetates having 4 functional groupsper molecule are1,4-butanediol diacetoacetate, 1,6-hexanedioldiacetoacetate, neopentyl glycol diacetoacetate, cyclohexane dimethanoldiacetoacetate or ethoxylated bisphenol A diacetoacetate.
 8. Thecomposition of claim 1 wherein acetoacetates having 6 functional groupsper molecule aretrimethylol propane triacetoacetate glycerintriacetoacetate polycaprolactone triacetoacetates.
 9. The composition ofclaim 1 wherein acetoacetates having 8 functional groups per moleculeare pentaerythritol tetraacetoacetate.
 10. The composition of claim 9wherein said base is diazabicycloundecene (DBU).
 11. The composition ofclaim 1 wherein said reaction between a Michael donor acetoacetate and aMichael acceptor acrylate occurs in the presence of non-reactivesolvents.
 12. The composition of claim 11 wherein said solvent isstyrene, t-butyl styrene, α-methyl styrene, vinyl toluene, vinylacetate, allyl acetate, allyl methacrylate, diallyl phthalate, C₁ -C₁₈methacrylate esters, dimethacrylates or trimethacrylates.
 13. Thecomposition of claim 12 further crosslinked in the presence of a freeradical generating catalyst.
 14. The composition of claim 12 furthercomprising a photoinitiator.